Acute kidney injury (AKI) is a critical clinical problem. The annual prevalence of AKI is 22-620 per million populations in the USA. In particular, the AKI incidence is extremely high in critically ill patients with high mortality. Current overall mortality is still unacceptably high at ~ 30%. Even if patients survive the acute insult, long-term prognosis after AKI is still far from optimal. Of surviving patients, 5-20% are still dialysis-dependent at hospital discharge. The prevalence chronic kidney disease (CKD) is currently estimated at 26 million (16.5%) Americans. Of note, a significant number of CKD patients have a history of AKI. Furthermore, patients with pre-existing CKD are more susceptible to renal insults and have a poorer outcome and higher mortality when they develop AKI. Thus, efficient treatment of AKI is an effective modality to block the development of CKD. Hypoxia-inducible factor (HIF) is a heterodimeric transcription factor that regulate(s) many genes involved in angiogenic, metabolic, and oxygen transport functions. HIF1/2 activation protects the kidney from IRI. Erythropoietin (EPO) has also been used for treatment of ischemic injury in the brain, heart, and kidney. Mice null for either EPO or EpoR have delayed tissue regeneration post ischemia, which suggests that EPO-EpoR is protective against hypoxic brain injury and heart injury. But the EpoR effect on AKI is relatively poorly documented. Moreover, the relationship of Klotho to HIF(s) and EpoR in the kidney is not defined. To date, renal replacement remains the sole treatment for AKI and improvement in outcome has been modest. Dialysis, though effective in maintaining body fluid composition and volume, is not able to ameliorate kidney damage and promote kidney regeneration. We found that Klotho is not only an early biomarker for AKI patients, but also confers renoprotection to attenuate kidney injury, and potentially promote recovery and prevent CKD development. Klotho protein may turn out to be a most promising protein for clinical AKI, but a lot of work still needs to be done. In this proposal, we propose a hypothesis that encompasses the existing database including our own preliminary data;and put it to test. Doubtlessly, this therapeutic study will provide more interesting and encouraging results to inspire to use Klotho protein as a novel strategy. We will also explore whether the mechanism of renoprotection by Klotho is through HIF(s) and EpoR. This data will set the stage for therapeutics as we are at an advanced stage of preclinical experimentation, placing us at a very close proximity to clinical testing. PUBLIC HEALTH RELEVANCE: Acute kidney injury is a critical clinical problem with high mortality. We use acute kidney injury rodent models to test the efficacy of Klotho protein and to define the mechanisms underlying Klotho renoprotection, in conjunction with cell culture work. The expected data will set the stage for Klotho treatment in AKI patients.